1. Field of the Invention
The present invention relates generally to missile tracking systems for tracking a target. More specifically, the present invention relates to a ball joint gimbal system for steering a gimballed mirror which is tracking a target.
2. Description of the Prior Art
A gimbal on a missile""s seeker is used to establish a line of sight vector between a target and the missile""s seeker. A visible or infrared sensor and associated optics are mounted on the gimbal. A narrow instantaneous field of view provides for long range tracking capability by the missile""s seeker. The motion of the gimbal provides for a large angle of regard to accommodate the need for target acquisition which is off boresight. The image received by the seeker is stabilized in inertial space to decouple missile body motion which reduces blur. The gimbal is movable in elevation and azimuth so that closed loop tracking occurs. The angular rate of motion of the gimbal is measured to facilitate closed tracking.
Generally gimbals allow for orthogonal elevation and azimuth motion by including an inner gimbal platform, a gimbal ring and an outer gimbal fork. The inner gimbal platform has a number of components mounted thereon including an imager and its associated optical elements such as a mirror, lens or prism which provide the image. Rate or free gyros are mounted on the inner platform to provide inertial stabilization for the gimbal. A gimbal IR sensor has a cryogenic cooler.
A gimbal ring is attached to the inner gimbal platform on a shaft to allow for rotary motion of the gimbal. A torque motor and angle transducer are attached to this shaft. An orthogonal shaft attaches the gimbal ring to the outer gimbal fork. A second torque motor and associated angle transducer are attached to this orthogonal shaft. In addition, wires and cooling lines run across the gimbal axes. This causes a coupling between the axes so that body motion isolation is difficult to achieve.
The gimbal structure is complex and the mechanical components are very precise. The conventional gimbal is therefore very expensive and also large and heavy making it difficult to mount in the confined space of a seeker.
Accordingly, there is a need for a low cost, yet highly effective gimbal which is adapted for use with a missile""s seeker.
The present invention overcomes some of the difficulties of the prior art including those mentioned above in that it comprises an inexpensive yet very accurate system for steering a gimballed mirror which is tracking a target being pursued by a missile in flight.
The ball joint gimbal system of the present invention provides for a precise line-of-sight stabilization of a gimballed mirror that rides on a ball and its associated support structure. The mirror is positioned by four braided lines. The brained lines are driven by four servo motor with each servo motor being coupled to one of four capstan shafts. Each of the braided lines is wound around one of the four capstan shafts. The braided lines are positioned by optical shaft encoders. The low inertia of the gimballed mirror and the positioning of the mirror by the braided lines result in an extremely accurate and fast scanning optical pointing system. Inertial gimbal stabilization of the line of sight to a target is by a stabilization algorithm utilizing body rate information from body sensors which are components of the missile for providing autopilot and navigation functions for the missile.
A digital signal processor receives externally generated steering signals from an external steering device, such as a joystick. The digital signal processor processes the signals to generate mirror position commands and provide the mirror position commands to the servo motor. The servo motors, responsive to the mirror position commands, continuously adjusting the length of each of the four braided lines to steer said gimballed mirror and maintain the line of sight to the target to continuously track the target.